Wireless communications devices, for instance, mobile phones, have become popular remarkably in recent years with their functions and services improved increasingly. Explanation will be made on a mobile phone as an example. There are various systems for mobile phones, for instance, GSM (global system for mobile communications) and DCS (digital cellular system) systems widely used mostly in Europe, a PCS (personal communications services) system used in the U.S., and a PDC (personal digital cellular) system used in Japan. According to recent rapid expansion of mobile phones, however, a frequency band allocated to each system cannot allow all users to use their mobile phones in major cities in advanced countries, resulting in difficulty in connection and thus causing such a problem that mobile phones are sometimes disconnected during communication. Thus, proposal was made to permit users to utilize a plurality of systems, thereby increasing substantially usable frequency, and further to expand serviceable territories and to effectively use communications infrastructure of each system. Thus, mobile phones adaptable to a plurality of systems are called multiband mobile phones, differentiated from single-band mobile phones adaptable to only a single system.
As conventional, small and light high-frequency circuit parts adapted to a plurality of systems, for instance, a dual-band, high-frequency switch module for use in mobile communications devices adapted to two systems of EGSM and DCS is disclosed in EP 0921642, and a triple-band, high-frequency switch module for use in mobile communications devices adapted to three systems of EGSM, DCS and PCS is proposed by EP 0998035.
FIG. 23 is a block diagram showing one example of a triple-band high-frequency switch module. A diplexer Dip connected to a terminal of a common antenna ANT causes branching to a signal in a frequency band of EGSM and a signal in a frequency band of DCS/PCS. The branching may be called “synthesis” in an opposite direction of a signal flow. A first high-frequency switch SW1 switches a transmission terminal Tx of EGSM and a receiving terminal Rx of EGSM, and a second high-frequency switch SW2 switches a transmission terminal Tx of DCS/PCS, a receiving terminal Rx of DCS and a receiving terminal Rx of PCS. Low-pass filters LPF1, LPF2 inserted into signal-transmitting lines suppress harmonics generated by high-power amplifiers. Bandpass filters SAW1, SAW2, SAW3 remove unnecessary frequency components from a receiving signal from the antenna ANT and send only necessary components to low-noise amplifiers. Accordingly, high-power amplifiers HPA1, HPA2 are disposed upstream of the transmission terminal Tx of EGSM and the transmission terminal Tx of DCS/PCS, and low-noise amplifiers LNA1, LNA2, LNA3 are disposed downstream of the receiving terminal Rx of EGSM, the receiving terminal Rx of DCS and the receiving terminal Rx of PCS.
With a still strong demand for making mobile communications devices smaller and lighter in weight, development has been progressing to have common parts and integrate functions into modules. For instance, circuit parts encircled by the dotted line in FIG. 23 are integrated into a multiband antenna switch module ASM, which is obtained by forming electrode patterns for transmission lines and capacitors on dielectric sheets made of LTCC (low-temperature cofired ceramics), etc., laminating them, and mounting diodes, etc. onto the resultant laminate. As modules in a range encircled by the chain line, there are, for instance, discrete SAW filters mounted onto the laminate.
Used on the side of the transmission of the mobile communications device is a high-power amplifier of about several watts for outputting a signal of a relatively large power, which may be called “high-frequency amplifier,” “power amplifier,” or simply “amplifier.” Because cell phones, etc. should be small and low in power consumption, the high-power amplifier consuming most of a DC power is required to be small and have a high DC-RF power-adding efficiency. Particularly, an important features of cell phones, etc. are that they are small and have long call time per one charge. Accordingly, the miniaturization and higher efficiency of the high-power amplifier are necessary. However, circuit parts containing high-power amplifiers have not been formed into a single laminate module.
As an antenna switch module, an antenna apparatus comprising an antenna exclusively used for receiving and amplifiers mounted onto a laminate with phase-adjusting circuits disposed therebetween is disclosed in JP 2000-183612 A. However, this antenna apparatus is to adjust the phase deviation of a closed loop when electromagnetic waves leaked from amplifiers are received by the antenna exclusively used for receiving (patch antenna), but to integrate high-frequency switch functions.
EP 0837516 discloses a module comprising transmission lines and capacitors for constituting high-frequency switches and amplifiers, which are formed in a multilayered board constituted by a laminate of a plurality of dielectric layers, and transistors, etc. mounted onto the multiplayer board. However, this reference teaches nothing about problems arising when the high-frequency switches and the amplifiers are integrated, and their solution means.
JP 2002-171137 A discloses a high-frequency transmission module in which a high-power amplifier and a coupler for monitoring the output power of the high-power amplifier are integrated, and both are set to be nonconjugate matching at a spurious frequency. However, this reference does not teach any specific means for solving the deterioration of the characteristics of reducing insertion loss between the high-frequency parts and harmonic attenuation characteristics.
As described above, no proposal has been made so far with respect to the integration of multiband antenna switch circuits and high-frequency amplifying circuits in one laminate as a composite module. What has been carried out so far is only that the already existing high-frequency amplifying circuits and the already existing antenna switch modules are variously combined to monitor transmission characteristics and antenna output characteristics such as conversion efficiency and the generation of harmonics, etc., thereby selecting good combinations of the parts.
When the high-frequency amplifier HPA and the antenna switch module ASM are combined in a laminate (ASM+HPA in FIG. 23), there are the same problems as when discrete parts are combined. Though an output terminal of a high-frequency amplifier and a transmission terminal of an antenna switch module are designed to match at 50 Ω, each part is not necessarily set to be 50 Ω strictly, but actuary set to be around 50 Ω. For instance, even if the high-frequency amplifier HPA and the antenna switch module ASM are 45 Ω with a phase position of 120° and 52 Ω with a phase position of 80°, respectively, it may be regarded that they are matching to each other at 50 Ω. In sum, though the conventional technology seeks matching at around 50 Ω, which is at a center of the Smith chart, in a transmission band, it does not take reactance into consideration. Without a specific guideline for the phase matching, it would be likely that there is large loss in a necessary fundamental frequency band, and that attenuation is insufficient in an unnecessary frequency band such as a second harmonic, a third harmonic, etc. This problem occurs even in a case where a high-frequency amplifying circuit and an antenna switch module are separately mounted onto a circuit board, with a matching circuit therebetween.
In addition, wide-band matching with low insertion loss in a transmission band is desired in a high-frequency module. However, even when the wide-band matching is sought only by an antenna switch module, the wide-band matching is not achieved in many cases in the entire high-frequency module comprising the high-frequency amplifier. This is because the input impedance Z4 of an output matching circuit in the high-frequency amplifier changes by a load (in this case, antenna switch module) connected to the downstream side of the high-frequency amplifier (see FIG. 10).